Subterranean piping systems such as are typically found at service stations are installed and connected to fuel dispensing pumps so as to provide dispensing of fuels from a fuel storage tank or tanks, usually installed below ground, to fuel dispensers, which are located above ground.
Conventionally, such underground piping systems comprise single wall pipes which are connected together on the site using standard straight pipes and associated fittings such as tees, 90.degree. elbows, 45.degree. elbows, and unions.
The underground storage tanks, the associated piping systems, and the fuel dispensers have all been determined to be sources of environmental pollution, as well as safety hazards because of leakage into the surrounding earth. Fire, explosions, and pollution of ground water have occurred because of these leakages.
With respect to the problem of leakage from underground fuel storage tanks, one solution has been to use double wall tanks, rather than conventional single wall tanks. Double wall steel tanks and double wall fiberglass tanks which are used to remedy this problem (together with a secondary containment and corrosion protection for the tanks) are disclosed in U.S. Pat. Nos. 4,568,925 (Butts) and 4,672,366 (Butts). The secondary containment system disclosed in these patents is applied to a conventional steel tank and creates a unique double wall tank referred to as a "jacketed steel tank". In the event of a leak in the inner primary tank, the leak is contained in the outer secondary tank. Most such double wall tanks are equipped with a leak detection device for signalling an alarm, in the event that a leak should occur.
While such tanks provide a partial solution, it has been determined that a substantial percentage of leakage which occurs at a typical service station site is due to leakage from the underground piping system. Various attempts have been made to deal with this problem. One approach is to install the piping in a trench line with a fuel impervious membrane liner or semi-rigid trough. This technique, if carefully installed, can provide a measure of containment of leakage from the piping system. However, such an approach does not offer truly effective leak detection. In particular, this technique does not permit a determination of when the leak occurred, or of the pipeline in which the leak is located, or of where in a specific pipeline the leak occurred. With such a system, should a leak occur, it may be required that all of the backfill contained within the trench or liner be removed. Further, integrity testing of such a system, by means of air pressure testing, is not possible. Further, in general, such systems do not provide 360.degree. containment and thus fill with water, thereby eventually becoming ineffective.
A further solution to the problem of leakage from piping systems involves the use of fiberglass primary piping from the pump of the underground storage tank to the above ground fuel dispenser, this piping being encapsulated with an outer secondary fiberglass pipe and with fittings that are installed simultaneously with the primary pipe. The secondary pipe is, of necessity, of a larger diameter than the primary pipe so as to enable the secondary pipe to slide over the smaller primary pipe. The secondary fittings are of a clam shell design adapted to fit over primary fittings after the primary pipe has been bonded together, integrity tested and inspected. Secondary fittings are bonded to the secondary pipe by a combination of nuts and bolts, and through the use of fiberglass resins or a fuel resistant sealant. Such a solution does not permit a complete inspection of the entire primary piping system during an air pressure integrity test. Due to the construction and design of this system, the limited components available, and the bonding techniques used, it is difficult to install a system of this type which is air pressure testable. Further, the components of this system are expensive to make as well as expensive to install.
General considerations, and both present and future regulatory requirements for primary piping, dictate that the piping possess a number of basic characteristics and meet a number of general design criteria. In this regard, the secondary containment system should be of such a design that the secondary system contains the primary system from the dispenser to the tank including the submersible pump housing and all swing joints. In addition, the secondary containment system should allow for complete inspection of the primary pipe fittings during an air pressure soap test, before the secondary pipe system is completed. Further, the secondary containment system should be compatible with the products to be stored. In addition, the secondary containment system should be non-corrosive, dielectric and non-degradable, and should be resistant to attack from microbial growth. Still further, the secondary containment system, the materials used therein and the design thereof, should be of sufficient strength to withstand the maximum underground burial loads. In addition, the secondary containment fittings should be capable of being installed over the primary fittings after completion, testing and inspection of the primary piping system is complete so as to allow inspection of the primary fittings during such testing. Further, the secondary containment system should have a monitored fuel collection sump at the low end of the system which provides a fitting for insertion of a continuous monitoring sensor for signaling an alarm should a leak occur in the primary piping.